Television apparatus



March 26, 1946. H. T. LYMAN TELEVISION APPARATUS Filed Aug. 18, 1945Fig.1.

Inventor"- Harold T. Lyman, x]

Has Attorney Patented Mar. 26, 1946 UNITED General Electric Company, a

New York corporation or Application August 18, 1943, Serial No. teams 7claims. (01. 315G422) My invention relates to television apparatus ofthe type employing a cathode ray picture tube and particularly tocircuits for supplying high unidirectional voltages to the anodes of thecathode ray tubes in such apparatus.

It is an object of my invention to provide an improved high voltagegenerating circuit of small size and light weight for supplying theunidirectional voltage for the anodes of cathode ray tubes.

It is another object of my invention to provide on improved circuit fortelevision apparatus or the like for providing high unidirectionalvoltages for the anodes of cathode ray tubes which shall result inminimum interference with the operation of the associated circuits.

The features of my invention which I believe to be novel are set forthwith particularity in the appended claims. My invention itself, however,

both as to its organization and method ofopera tion together withfurther objects and advantages may best be understood by reference tothe following description taken in connection with the accompanyingdrawing in which Fig. 1 diagrammatically represents one fgm oftelevision apparatus embodying my invention, and Fig. 2 representscurves showing certain characteristics of the ap paratus of Fig. 1.

Referring nowto Fig. l, I have shown a portion of a television apparatuswhich, for example, may be a television receiver, and which includes acathode ray electron discharge device or tube It. The tube I is providedwith an electron gun ineluding a cathode H, a control electrode or gridl2 and an anode [3. A second anode It comprising an annular metalliccoating on the inner surface of the tube is provided to accelerate theelectrons projected from the cathode and to aid in focusing the beam.The tube I0 is also provided with horizontal and vertical deflectingmembers It and I6, respectively, which have been illustrated as coilsfor deflecting the beam magnetically. Composite television picture andsynchronizing signals are received and detected by suitable apparatus(not shown) and the picture or video signal is supplied by a suitableamplifier l8 connected to impress the picture signal between the controlgrid 12 and the cathode I I of the oathode ray tube to control theintensity of the electron beam in the usual manner. The horizontaldeflecting coil I is supplied with a saw-tooth our- 1 rent wave from asuitable saw-tooth generator (not shown) which is synchronized in theusual manner. The saw-tooth wave produced by the generator is amplifiedby an electron discharge device It and is supplied to the coil Hi fromthe secondary oi. a transformer 2i! the primary of which is connected inthe load circuit of the device it. A similar deflection circuit (notshown) is provided to energize the vertical deflection coil t6.

For satisfactory operation of the tube It) it is necessary that theanode I l be supplied with very high unidirectional voltage which may beof the order of 7500 volts or higher. In order to supply the highvoltage for the anode Hi I provide an air core induction coil orautotransformer 22 having an electron discharge device 23 connected tosupply current to its primary circuit. The device 23 includes a cathode2 5, a control grid or electrode 25, a screen grid 28 and an anode 2?. Asuitable source of direct current potential such as a battery 28 isconnected to the anode 2? through the primary of the transformer 22 andthe screen grid 26 is connected to the battery 28 through a suitableresistance 3d. The device 23 is normally conducting so that asubstantial current flows through the primary of the transformer 22. Inorder to produce a high voltage across the secondary of the transformer22 the current through the primary is interrupted intermittently toproduce a high rate of change of flux through the transformer coil toinduce a high voltage across the coil. A rectifier tube Si is connectedacross the autotransformer to rectify the voltage and supply it to asmoothing filter comprising condenser-s 32 and 33 shunting a resistance3 the filter being connected to the anode it oi. the cathode ray tube tosupply the necessary high umdirectional voltage.

It is desirable that transient voltages existing in the circuit duringthe generation of the high voltage should be prevented from causinginterference with the picture signal. For this reason the tube 23 is cutoff to produce the high transient voltage only during the retrace periodwhen no picture signal is being transmitted. In order to accomplishthis, the control grid 25 is connected through a resistor 35 to thesecondary of the transformer 20. The voltage appearing at the secondaryof the transformer 20 comprises a series of steep pulses of negativepolarity produced by the sudden rate of change of current in thesecandary circuit during theretrace periods. These negative pulses areemployed to cut ed the tube 23 during the retrace periods so that thetransient voltages appearing in the high voltag generating circuitsoccur only during the retrace periods and do not produce interferencewith the picture signals.

The magnitude of the effective unidirectional voltage is substantiallyincreased by employing the air core autotransformer (i2 d ioar'ticuiarlyby tuning the transformer coil Wit associated therewith so that sevloscillations occur during the retrace period. capacities include thecapacity of the rectifier tube, the plate circuit capacity of the tubeand the distributed capacity of the coil 22. The rectifier ill includesan anode 38 connected. to the coil 22 and a cathode 3? connected to theresistance to of the filter. Heatlng'current for the cathode is derivedfrom the transformer 22 through a secondary coil or comprising about twoturns, the transformer 22 usually having several thousand turns.-

A further understanding of the operation of the circuit may be obtainedupon reference to Fig. 2 in which curves til, to, ll and t2 represent,respeotively, the current through the deflection coil iii, the voltageat the deflection coil terminal, the voltage across the transformer 22,and the relate current of the tube fit. Thesecurves are plottedcanacities on the same vertical time axis and represent one 7 cycle ofoperation. The steep retrace portion of the current curve as indicatedat too produces a steep negative pulse iller in the voltage curve toduring the retrace period, the remainder of the curve lit beingsubstantially fiat since the trace portion oi the current curve has asubstam tially constant rate of change. The negative pulse tile whenapplied to the control grid to of the tube cuts oil the flow of currentthrough the tube and therefore, through the primary circuit oi thetransformer 22. This sudden rate of change of current through theprimary circuit produces a high voltage surge in the transformer and,slncethe transformer is tuned. to a frequency sufficiently high toproduce several oscillations during the retrace period, a voltage curveas incl-- cated at tie is produced, this voltage being the stepped upvoltage across the secondary circuit of the transformer. $ince thetransformer is connected to the plate of the rectifier tube, only thepositive portions of the oscillation Wave produce a flow of currentthrough the rectifier and a high positive voltage is applied to theanode it of the cathode tube. The value of this voltage is substantiallythat of the positive peak of the oscillation curve Hit, the condenser 32being charged to this voltage and substantially maintaining its chargeduring the trace period of the Wave when the rectifier isnon-conducting. The transformer coil is is lightly damped during theretrace period when the electron discharge device '23 is non-conducting.However, upon the termination or the negative pulse the, the resistanceof the tube 23 falls and produces heavy damping of the coil 22. Thisinsures one or more complete oscillations during retrace and preventsthe continuation of the oscillations during the trace period of thesaw-tooth wave and minimizes interference with the picture signals whichmight otherwise result from the generation of the high voltageoscillations.

The high voltage generator described above may be constructed to occupyan extremely small space and weighs very little since it does notrequire a heavy iron core transformer. The coil 22 has a high Q, thatis, a high ratio of stored energy to dissipated energy which isdetermined by the ratio of the reactance of the coil to its resistance.It is, therefore, apparent that the circuit of Fig. 1 makes it possibleto construct an extremely high voltage generator of small dimensions andlight weight which is particularly useful in apparatus such astelevision receivers Where space is limited.

In television apparatus and the like in which the frequency of the waveapplied to the sweep coils iii is of the order 01' several thousandcycles per second or higher, the time constant of the filter 32, Wand 84can be made sufllclently low so that the energy storage in 32 and 33 isfar below the dangerous limit for bodily contact. In a typical case of atelevision receiver 32 and '33 can be of the order of up. i'd. each and34 can be of the order of 0.25 megohm. Direct contact produces no morethan a slight burn even though the voltage is or the order or 7500 voltsbecause the stored energy is low and the regulation of the supply isvery severe above a current of 2 milliamperes. The capacity 33 may inthe case cited be the conductor-to-shield capacity of the high voltageanode connecting cable usually employed with such circuits.

Whilel have illustrated one embodiment of my invention in connectionwith a television receiving oircuitemploying magnetic deflectingmembers, other modifications and applications will readily occur tothose skilled in the art. I do not, therefore, desire my-invention to belimited to the particular embodiment illustrated and described and Icontemplate by the appended claims to cover all modifications which fallwithin the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a television apparatus or the like a cathode ray electrondischarge device having an anode and a ray deflecting member, means forimpressing on said member a saw-tooth deflecting wave having a rapidretrace portion, an electron discharge device, an air core inductionc011 connected in the output circuit of said device, means dependentupon the retrace portion of said sawtooth wave for intermittentlycutting off the flow of current through said coil to produce a highvoltage surge, and means including a rectifier connected in series withsaid coll for producing a high unidirectional voltage, said coil beingtuned to produce several high voltage oscillations during the retraceportion of said wave whereby the maximum unidirectional voltage iseiloctlvely increased.

2. In a television apparatus or the like, a cathode ray'electrondischarge device having an anode and. a ray deflecting member, means forimpressing on said member a saw-tooth deflecting wave having a rapidretrace portion, an air core induction coil, means including an electrondischarge device having a cathode and an anode and a control electrodefor producing a flow of current through said coil, means for derivingnegative pulses from the retrace portions of said wave and forimpressing said pulses on said control electrode intermittently to cutoff the flow of current through said coil whereby high voltage peaks areproduced across said 0011, said coil being tuned to produce severalretrace portion of said wave, and means including a rectifier connectedin series withsaid coil for producing a high unidirectional voltage.

3. In a. television apparatus or the like, a cathode ray electrondischarge device having an anode and a magnetic ray deflecting coil,means for producing in said coil a. saw-tooth current wave having arapid retrace portion whereby a high negative voltage pulse is producedat said coil during the retrace portion, an air core induction coil,means including an electron discharge device for producing a. flow ofcurrent through said oscillations during 7s coil, means utilizing saidnegative pulse for com trolling said device intermittently to cut oilthe flow of current through said coil whereby high voltage peaks areproduced across said coil, said coil being tuned to produce severaloscillations during the period of interruption f the flow of currenttherethrough, and means including a rectifler connected with said coilfor producing a high unidirectional voltage and for applying saidunidirectional voltage to said anode.

4. In a television apparatus or th like, a cathode ray electrondischarge device having an anode and a ray deflecting member, means forimpressing on said member a saw-tooth deflecting wave having a rapidretrace portion, an air core autotransformer, means including anelectron discharge device for producing a flow of current 7 through theprimary circuit of said transformer, means dependent upon the retraceportion or said saw-tooth wave for intermittently cutting ed the flow ofcurrent through said device to produce a high voltage surge in saidtransformer, and means including a rectifier connected in the secondarycircuit of said transformer for producing a high unidirectional voltageand for applying said unidirectional voltage to said anode.

5. In a television apparatus or the like, a cathode ray electrondischarge device having an anode and a ray deflecting member, means forimpressing on said member a saw-tooth deflecting wave having a rapidretrace portion, an air core autotransformer, means including anelectron discharge device for producing a flow of current through theprimary circuit of said transformer. means dependent upon the retraceportion of said saw-tooth wave for intermittently cutting off the flowof current through said device to produce a high voltage surge in saidtransformer, and means including a rectifier connected in the secondarycircuit of said transformer for producing a high unidirectional voltageand for applying said unidirectional voltage to said anode, saidtransformer as connected to said circuits havin a natural period ofoscillation such that several oscillations occur during the retraceportion of said wave whereby the maxiumum uidirectional' voltage iseffectively increased.

6. In a television apparatus or the like, a cathode ray electrondischarge device having an anode and a ray deflecting member, means forimpressing on said member a saw-tooth deflecting wave having a rapidretrace portion, an electron discharge device, an air core inductioncoil connected in the output circuit of said device, said coil beinglightly damped when said device is nonconducting and heavily damped whensaid device is conducting, means dependent upon the retrace portion ofsaid saw-tooth wave for intermittently cutting oil the flow of currentthrough said coil to produce a high voltage surge, and means including arectifier connected in series with said coil for producing a highunidirectional voltage, said coil being tuned to produce several highvoltage oscillations during the retrace portion of said wave whereby themaximum unidirectional, voltage is effectively increased; saidoscillations being effectively stopped by the heavy damping of said coilat the end of said retrace portion when said device becomes conducting.

7. In a television apparatus or the like, a cathode ray electrondischarge device having an anode and a ray deflecting member, means forimpressing on said member a saw-tooth deflecting wave having a rapidretrace portion, an air core autotransformer, means including anelectron discharge device for producing a flow of current through theprimary circuit oi said transformer and for efiecting heavy damping ofsaid transformer, said transformer being lightly damped when said deviceis noncondu'cting, means dependent upon the retrace portion of saidsawtooth wave for intermittently cutting of! the flow of current throughsaid device to produce a high voltage surge in said transformer, andmeans including a rectifier connected in the secondary circult of saidtransformer for producing a high unidirectional voltage and for applyingsaid unidirectional voltage to said anode, said transformer as connectedto said circuits having a natural period of oscillation such thatseveral oscillations occur during the retrace portion of said wavewhereby the maximum unidirectional voltage is effectively increased,said oscillations being effectively terminated by the heavy damping ofsaid autotransformer when said device becomes conducting at the end ofsaid retrace portion.

HAROLD T. LYMAN.

